Nowadays where electrostatic paint applicators are in widespread use, such machines having a rotary atomizer head are widely used in the field of car body coating, for example. These paint applicators are called rotary-atomization-type paint applicators. As disclosed in Patent Documents 1 to 8, the rotary atomizer head is an assembly of an atomizer head body and a functional member disposed in a central portion of the atomizer head body. Paint is supplied to the rotary atomizer head through a feed tube, and atomized by the rotary atomizer head that rotates at a high speed. For this intended role of the rotary atomizer head, it is required to have a highly precise rotational balance.
For internal cleaning of the rotary atomizer head, there have been developed techniques for easier disassembling and reassembling of the rotary atomizer head. Patent Document 1 discloses a rotary atomizer head that is configured to attach the functional member to the atomizer head body by access from behind. It is proposed in Patent Document 1 to form a paint outlet in the atomizer head body and to make a paint chamber of the rotary atomizer head, which is a chamber for receiving paint supplied from a feed tube, by cooperation of the atomizer head body and the functional member attached to the atomizer head body from behind.
Patent Documents 2 et sec. disclose rotary atomizer heads configured to attach a functional member called a “hub member” to the atomizer head body by access from its front face. Patent Document 2 proposes to fix the hub member in a central recess of the atomizer head body via an elastic ring. More specifically, the rotary atomizer head disclosed in Patent Document 2 has a circumferential groove (first circumferential groove) formed in a circumferential wall surface of the central recess of the atomizer head body and another circumferential groove (second circumferential groove) formed in a circumferential surface of the hub member. By laying the elastic ring in the first and second circumferential grooves to be commonly grasped by these grooves, the hub member is removably fixed to the atomizer head body.
With the rotary atomizer head disclosed in Patent Document 2, the hub member can be easily removed from the atomizer head body for the purpose of cleaning, and attached again to the atomizer head body after completion of the cleaning.
Patent Document 3 discloses another existing rotary atomizer head that can be disassembled and reassembled. The rotary atomizer head disclosed in Patent Document 3 has a step formed at the front end of the peripheral wall of the central recess of the atomizer head body, and a disc-shaped hub member fittingly engages with this step. More particularly, the disc-shaped hub member has elasticity and flexibility owing to natures of its shape and material, and it can get in fitting engagement with the step of the atomizer head body with the elasticity and flexibility. Further, a retaining circumferential ridge is formed on the circumferential surface of the step of the atomizer head, or the circumferential surface of the step is tapered to decrease its diameter forward, as a measure for preventing the hub member from being disengaged forward of the atomizer head body. Further, Patent Document 3 discloses a rotary atomizer head having a spoon-cut groove formed in the bottom of the central recess of the atomizer head body and having an inclined wall surface extending continuously from the spoon-cut groove and enlarging its diameter gradually forward. The above-mentioned disc-shaped hub member has a plurality of paint outlets formed to align concentrically in the outer circumference thereof. The paint outlets extend tangentially to the inclined wall surface.
Patent Document 4 proposes to attach permanent magnets on a disc-shaped hub member and an atomizer head body for receiving the hub member, such that the disc-shaped hub member can be fixed to the atomizer head body with the attraction of the permanent magnets.
Patent Document 5 proposes to use a disc-shaped hub member having a number of legs, which can be removably fixed to the atomizer head body by engagement of free ends of the legs with a circumferential groove in the central recess of the atomizer head body in order to removably secure the hub member to the atomizer head body. In addition to this, Patent Document 5 proposes to provide a clearance between the outer circumference of the disc-shaped hub member and the atomizer head body to use it as a paint passageway.
One problem of the rotary atomizer head disclosed in Patent Document 2, which relies solely upon a resistance force produced by the elasticity of the elastic ring for fixing the hub member to the atomizer head body. Another problem of this rotary atomizer head, which relies on the elasticity of the elastic member for fixing the hub member in position, is a difficulty for a user to be sure that the hub member has taken its proper position when he should attach it to the atomizer head body. Still another problem of this atomizer head is that the elastic ring deforms when the rotary atomizer head rotates at a high speed, and thereby degrades in its sealing performance.
To interpose the elastic ring between the atomizer head body and hub member means that a relatively large clearance exists between the atomizer head body and hub member. Therefore, the technique proposed by Patent Document 2 can be considered to admit inrush of paint through the clearance. When paint should be changed to another color, the rotary atomizer head needs internal cleaning without being disassembled. However, it is difficult to remove paint having entered the clearance between the atomizer head body and the hub member by the internal cleaning. Because of this and other reasons, the invention disclosed in Patent Document 2 has not yet been put into practice.
Patent Document 3 proposes to put the disc-shaped hub member in fitting engagement with the step portion of the atomizer head body and to form the retaining circumferential ridge on the circumferential surface of the step portion of the atomizer head, or to taper the circumferential surface of the step to decrease its diameter forward, as a measure for preventing the hub member from being disengaged forward of the atomizer head body. This invention of Patent Document 3 has not yet been put into practice as well.
Patent Document 4 proposes to secure the disc-shaped hub member and atomizer head body to each other by the attraction force of permanent magnets. Because of this structure, this technology is disadvantageous in that the materials of the disc-shaped hub member and the atomizer head body are limited to nonmagnetic ones (aluminum).
In Patent Document 5, it is disclosed that the disc-shaped hub member is fixed by engagement of the legs of the hub member with the circumferential groove formed in the peripheral wall of the central recess of the atomizer head body and that paint outlets are formed in each interval between every adjacent legs in the clearance between the outer circumference of the disc-shaped hub member and the peripheral wall of the central recess. Therefore, when the rotary atomizer head is cleaned with a cleaning liquid supplied to the rotary atomizer head, paint having adhered to the circumferential groove and legs will remain unremoved. Because of this problem among others, Patent Document 5 explains in detail how to remove the hub member from the atomizer head body when the atomizer head should be disassembled for cleaning.